Carbon nanotubes (CNT) have been the subject of intense research since their discovery in 1991. CNTs possess unique properties such as high surface to volume ratio and high electrical conductivity, which makes them suitable in a wide range of applications, including use as structural materials in molecular electronics, nanoelectronic components, and field emission displays. Carbon nanotubes may be either multi-walled (MWNTs) or single-walled (SWNTs), and have diameters in the nanometer range.
Because of their size and electronic properties, nanotubes show promise as components of nano-scale electronic devices. However, nanotubes are produced in a wide distribution of diameters and chiralities. Larger diameter nanotubes are generally more suitable for use as interconnects in such devices. Therefore, a method to isolate nanotubes of a minimum size is needed.
Hassanien et al (Nanotechnology, 16, (2005), 278-281) and Zhang et al (JACS 128, (2006), 6026-7) describe the reductive etching and cutting of SWNTs using hydrogen and hydrocarbon plasmas. Oxidative treatment of CNTs have been performed by several researchers. Seo et al (JACS 125, (2005) p13946-7) demonstrated that under their conditions CO2 attacks preferentially zigzag nanotube edges, therefore selecting for armchair nanotubes. Green et al (U.S. Pat. No. 5,346,683) reacted MWNTs with CO2 and other gasses and demonstrated that the gas reacted with the capped regions of the nanotubes only.
Applicants have discovered a method to remove any type of SWNT of specified diameters using CO2.